Print shops also typically have color definitions that apply to specific processes that you should follow for a job.

For example, dark blacks in print. In CMYK, where K is basically black, going 0/0/0/100 is not a very dark black. It needs other colors mixed in. But if you do too much, you can wind up with a black that's too richly mixed and won't dry properly, and wind up smearing and ruining your prints.

A print shop will typically have a specific CMYK mix you should use for the richest black without fucking things up, that looks something like 30/30/20/100. They will also often use something like 0/0/0/100 to define what is essentially an alpha layer for some other process layer like gloss or glitter or embossing. You provide a layer of the design where black is what gets embossed and white is what doesn't, for example.